Hi, I keep having to replace a 400 watt dimmer switch which controls 8 recessed lights fitted with 50 watt GU10 lamps, every time a lamp blows ( once a month on average) the dimmer fails and has to be replaced. Any ideas on what could be the cause and how to remedy it would be welcome.

Its a common problem with dimmers, thyristors/triacs are susceptible to damage by surges when a lamp blows due to that good old plasma arc.

In real terms the thyristor;/triac must have 2.5 times greater than the current rating of the fuse to survive, the answer is either buy an expensive dimmer module that has an inline fuse, fit an inline fuse in the module or keep buying dimmer modules.

regards

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"Take nothing but a picture,leave nothing but footprints!"-------------------------"Oh! The drama of it all."-------------------------"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"-------------------------

You may find that the dimmer is not compaitble with GU10 lamps. 8 off 50W lamps represents 400W of load. The dimmer may need to be rated at about 800W!! The lamps are 'reactive' and you will need a dimmer rated in excess of the load.

In the past when I have seen this type of failure, on speaking to a number of manufacturers, I have found that they will not 'support' the use of dimmer switches with GU10 lamps.

A further thought, you may need to ensure that the lamps are internally fused. Alledgedly, the cheap lamps from the supermarkets are not and consequently cause the dimmer to fail when the lamp fails.

I learned recently that the internally fused lamps have a 'C' after GU10, a customer of mine got some off the internet somewhere, might be worth Googling GU10-C. I don't know if these always prevent the dimmers from damage when the lamps fail, I only fitted them a couple of months ago, haven't heard anything since!

Even fitting lamps with fuses, it is possible that the dimmer may still fail. At the moment, the design accounts for 100% of the dimmer's rated maximum capacity. Assuming that it is built to a price (and most are in my opinion), there may not be enough spare capacity to operate the fuse before the triac fails.

I can tell you from experience that this often has to be a problem you have to live with, a few years ago when the band I was with was gigging three to four days a weeks all over the place incl Europe and we had our own lighting rig I think RS used to love me because I was buying components a bag full at a time, I tried many options like up-rating the triac, SPD's and the suchlike but when a par went it still invariably took out the triac even though the equipment had a fuse that was supposed to blow.

I think you have to remember that the plasma arc that is created when a bulb goes is something like 40,000 to a million A^s thats a fair old whack for a discrete component, the amazing thing was it never used to affect the IC or the other components just the Triac.

regards

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"Take nothing but a picture,leave nothing but footprints!"-------------------------"Oh! The drama of it all."-------------------------"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"-------------------------